Can anyone advise me on this please?

When I log into Admin, I get the following php errors:
   Undefined index: zero_plural in ... /public_html/include/functions.inc.php on line 925
   Undefined index: day in             ... /public_html/include/functions.inc.php on line 520
   Undefined index: month in         ... /public_html/include/functions.inc.php on line 523

The site works OK, except that when I attempt to run a slideshow, I get more php errors:
   Undefined index: day in             ... /public_html/include/functions.inc.php on line 520
   Undefined index: month in         ... /public_html/include/functions.inc.php on line 523

I suspect these errors arise from some file corruption when transferring the web-site from one location to another.

Is there any way of doing a re-install/repair of Piwigo to remedy these problems?
Or is there any other way of fixing this?

Any help or suggestions would be very much appreciated.

Regards
Bob